The only reason to have it upside down, which is really right side down, is to be "original". We don't mess with the coil very often. So those who want to look correct are correct. Those who want to have better access, etc., are happy and incorrect. Coils are shown, in Chevy Truck manuals, with secondary tower downward, up to at least 1959 on 6 Cyl. The functionality of either way is subjective. (I like up)
Correct= like factory installed and shown in various old literature for the year of the motor engine.